The enzymatic activity of renin is increased in plasma of patients with hypertension and patients with chronic renal failure, possibly due to the deficiency of a circulating renin inhibitor. An acetone soluble lipid extract of plasma and two protein containing plasma fractions (a high protein and a low protein fraction) obtained by Sephadex chromatography inhibit renin. The overall objective of this project is to purify these renin inhibitors and to evaluate their functional significance. Protein purification of the renin inhibiting Sephadex fractions will be carried out to determine if: a) a renin inhibiting lipid is associated with a specific protein, and b) a renin inhibiting peptide can be identified. Steps in protein purification will include Sephadex chromatography, chromatofocusing, chromatography with DEAE cellulose and carboxymethyl cellulose, and HPLC. Renin inhibiting lipid extracts and lipids associated with renin inhibiting protein fractions will alsp be purified; the dependence of inhibition on lipid and/or protein will be determined. Neutral and phospholipids will be separated, and lipids will be further purified with GLC. Additionally, affinity chromatography using a Sepharose afffinity column with purified mouse submaxillary renin as ligand will be used to extract and purify renin inhibitors. In all experiments, renin inhibition will be determined in vitro by evaluating the effects of putative inhibitors on the rate of angiotensin I production after addition to renin-renin substrate and in vivo by evaluating their effects on the pressor response to renin in the anephric rat. The hypothesis that increased enzymatic activity of renin in plasma of hypertensive patients and patients with renal failure is related to the deficiency if a renin inhibitor will be evaluated. We will also evaluate the hypothesis that "activation" of renin by acidification of plasma if related to denaturation of a renin inhibitor. We will determine if increased concentrations of inactive renin in plasma of patients with diabetes mellitus is related to increased concentrations of an acid labile renin inhibitor. To further evaluate a physiologic role of renin inhibitors, we will determine if acute and chronic administration of renin inhibitors extracted from plasma lowers blood pressure in a renin dependent model of experimental hypertension. Identification of naturally occurring renin inhibitors will add a new dimension to current understanding of the renin-aldosterone system.